I think articles coming out ahead of the announcement, explaining to the general public what the announcement means is actually really helpful. Then more people who might be interested can turn in to the announcement itself.
For the official announcement, where you'll hear all of the sound bytes you'll be reading later today, you can get to the livestream from Caltech's website here https://www.caltech.edu/
I'm am really confused as to how Martin Rees has written such a poor article. He's bloody Astronomer Royal. I suspect a ghostwriter.
a) Gravitational waves do NOT "shake the mirrors". They make spacetime contract in orthogonal directions around and within the beam tube (and of course elsewhere) thus causing the light to travel a tiny bit further in the tube, thus causing interference by moving the two beams out of phase.
b) As I posted the other day - what about Virgo? What about GEO600? I feel really sorry for the scientists who've spent decades working on this as part of a global collaboration to now have LIGO take all of the credit for this discovery.
a) Saying "gravitational waves don't shake the mirrors, it's length contraction" is as confused as saying "the Sun doesn't pull on the Earth, it bends spacetime around it". In each case, you're describing the same mechanism with different words. The whole point of the equivalence principle is that gravitational forces are equivalent to changing the local inertial frame. Ultimately, the Einstein field equations are what they are, but both types of description in words are correct (and inexact).
b) Virgo and GEO600 didn't detect gravitational waves. LIGO did.
Blame the sub-editors at the Telegraph, what's left of them (or more accurately it's CE Murdoch MacLennan and the weirdo Barclay Brothers that own it). That paper has been on a gradual downwards trajectory in quality for a long time now, and it's rare thing that it produces anything resembling actual journalism.
It's gradually morphed from being a Times for mildly xenophobic Conservatives (big C) into a Daily Mail for toffs.
The author is Sir Martin Rees, the leading astronomer in the UK (Astronomer Royal), and former president of the Royal Society. It's not some random journalist.
It's common for journalists to be told science news before an official announcement if they agree not to publish on it until afterward. This is called an embargo.
How do they measure (not just calculate, if I understand this correctly) "a distance less than a millionth of the size of a single atom"? That sounds very difficult to do with equipment that is presumably made of atoms.
You can use "low-coherence interferometry" to measure tiny signals that would be undetectable otherwise. Combine a "reference" beam with a "signal" beam and you get a measurable interference pattern, even when the magnitude of the signal beam is miniscule.
This is what a real-life interference pattern looks like (I just acquired this from an actual interferometer illuminating a painted metal surface):
This is now an established medical imaging method (Optical Coherence Tomography) to create 3d scans of biological tissue. It can also be used to measure distance or elevation changes on a surface of anything from a micrometer-level scale to a planetary surface. All you need is to use light with the right wavelengths and two measurements "arms" of roughly the same length.
When light interferes with itself it creates a "pattern". When the light beams are out of phase, the interference pattern is different. The gravitational waves basically minutely increase the distance that one of the beams travels and causes it to go out of phase with the other, thus changing the interference pattern.
Seriously, the only thing this article is says: Physicists and astronomers are agog. On Thursday, experimenters will report the first detection of a phenomenon that has been long predicted: bursts of gravitational waves generated by cosmic collisions of black holes.
That is NOT a report, that's someone guessing what the report will be. There's not a single quote from anyone remotely involved in the project. This is a piece of shit summary of a wikipedia entry on LIGO with a clickbait headline.
The second paragraph, immediately afterwards, says:
"Sadly it is not unknown for hyped-up scientific claims to be mistaken or exaggerated - claims of particles going faster than light, gravitational waves from the big bang, and so forth. I count myself a hard-to-convince sceptic. But what is being claimed will be the culmination of literally decades of effort by scientists and engineers with high credentials, and this time I expect to be fully convinced."
ie., Sir Martin Rees (the author), one of the most famous astronomers in the world, is putting his credibility behind this. That matters.
You are a very skeptical, no BS, tough nut to crack kind
of guy. Good! I like that! HN,
the Internet, the world needs much more of
that. Such high standards make at least
some of HN a crown jewel of the Internet
place.
Still, back to common, ordinary, reality,
Sir Rees does have a lot of credibility.
"This is why it’s been crucial to have two similar detectors separated by nearly 2,000 miles - one in Washington State, the other in Louisiana - and to seek events that show up in both detectors, thereby ruling out effects caused by local seismic events, passing trucks, and so forth."
Sounds like a good old survival bias ;)
Seriously though, what is confidence interval in LIGO?
i want to take my upvote away from this. seeing the title, i foolishly thought that the conference already took place, and just clicked before reading and seeing that the title is a lie. :/
At the moment, it would tell us more about cosmology than about the underlying physics, were we not to detect the gravitational waves. We expect gravitational waves to be emitted from two black holes as they orbit very close to each other, just before they merge. From general relativity, we know how big of gravitational waves to expect. However, we don't know how many such black hole mergers occur in nearby space.
LIGO can only measure gravitational waves down to a certain strength, and so we can only detect waves that are caused by black hole mergers within some distance of Earth. Predictions of how many such mergers occur vary wildly, depending on the assumptions in the model. (I don't have exact numbers, and would appreciate if anyone does have the numbers.)
If we did not detect gravitational waves, I would use that as a lower bound of the number of black hole mergers, rather than as a breaking of general relativity.
Not observing any gravitational waves wouldn't prove that gravitational waves didn't exist, so there wouldn't be nearly as much fuss and news articles written. Imagine the press release: "Jury still out on existence of gravitational waves: LIGO not sensitive enough/ Is LIGO a gazillion dollar waste?." So while if someone were able to PROVE that gravitational waves didn't exist that would be pretty spectacular because it would upend decades of scientific research and cause us to rethink relativity.
But this is still pretty spectacular in it's own right. The predictions that physicists make are made by examining mathematical models that are only partially vetted. Some parts of the models remain theoretical because we don't have instruments sensitive enough to measure their predictions (we are talking about energies on a ridiculous tiny scale here). Finally we have invested millions on an instrument that is sensitive enough and it confirms (to the best of its ability) that we were on the right track. This is a great relief to the scientists that they don't have to go back to the drawing board and rethink all their models, plus it is a great victory for predictions made before the age of computers.
If they were not detected, that wouldn't necessarily say much unless you could demonstrate certainly that they also should have been. In which case, yes. Though, in actuality, the physics of gravitational waves have been indirectly observed previously [0], so it's not like it's still entirely in the realm of hypothesis.
I actually was sort of curious as to the opposite. What does it mean if gravitational waves (that we can detect) are extremely common and become fairly easy to detect with future technology given todays news?
The article says many expected LIGO to take much longer but it found it rather earlier equating it to beginners luck (I know the article is written for the layperson but it leaves much to be desired with that phrase).
You never know we could have telescopes that use Gravitational waves instead of light.
The general direction may be possible, but the source itself would not be. The compression is smallest parallel to the direction of the wave's travel, and is largest perpendicular to the direction of the wave's travel. LIGO measures a change in the difference between the lengths of the two arms, ad so it would be more sensitive to waves moving along one of the arms. It would not be at all sensitive to waves that are moving perpendicular to both arms.
Since there are two such facilities, located on different parts of the Earth, they may be able to compare the relative size measured by each facility, and narrow down a part of the sky. Since the facilities are relatively close to each other (only 2000 miles, 30 degrees along Earth's circumference), the margin of error would be very large.
Ideally, to localize the direction, you would have three facilities, each located at 90 degrees away from the other two, so that you have one facility "pointed" in each direction. Even then, it would only be able to narrow it down to 2 possible origins, as the direction of travel of the wave would not be measurable.
Anything that carries information is limited to the speed of light. Gravitational waves carry information about the location of the merging black holes, and so they are limited to the speed of light. If anything that carried information were to travel faster than the speed of light, it would break causality, because you could find some frame of reference in which the effect happened before the cause.
And yes, it is spacetime itself that is vibrating.
If at the same time* we were to observe a supernova via other telescopes, that would give a pretty good indication. :)
*: And this would also possibly serve to answer another question -- do gravitational waves travel at precisely the speed of light? (also, I'd be interested in hearing about neutrino detectors -- how closely (if nonzero) to the speed of light do neutrinos travel?)
Shouldn't we have multiple detectors, to determine which direction the waves are coming from? (Like an antenna array can also be direction-specific using computational techniques).
Or are these detectors already directionally sensitive?
LIGO is based on two detectors, one in Louisiana and one in Washington. With those, according to today's talk, we can get a rough idea of the direction of the source: it was in the southern sky, vaguely in the direction of the Magellanic Clouds. Once some of the other planned experiments come online over the next few years, they expect to be able to localize sources to within 5-10 degrees on the sky. (Or so I just heard from the press conference.)
[+] [-] kbart|10 years ago|reply
[+] [-] ebbv|10 years ago|reply
[+] [-] jug|10 years ago|reply
;)
[+] [-] trymas|10 years ago|reply
[+] [-] __mbm__|10 years ago|reply
Starts in 2 minutes.
[+] [-] madaxe_again|10 years ago|reply
a) Gravitational waves do NOT "shake the mirrors". They make spacetime contract in orthogonal directions around and within the beam tube (and of course elsewhere) thus causing the light to travel a tiny bit further in the tube, thus causing interference by moving the two beams out of phase.
b) As I posted the other day - what about Virgo? What about GEO600? I feel really sorry for the scientists who've spent decades working on this as part of a global collaboration to now have LIGO take all of the credit for this discovery.
[+] [-] jessriedel|10 years ago|reply
a) Saying "gravitational waves don't shake the mirrors, it's length contraction" is as confused as saying "the Sun doesn't pull on the Earth, it bends spacetime around it". In each case, you're describing the same mechanism with different words. The whole point of the equivalence principle is that gravitational forces are equivalent to changing the local inertial frame. Ultimately, the Einstein field equations are what they are, but both types of description in words are correct (and inexact).
b) Virgo and GEO600 didn't detect gravitational waves. LIGO did.
[+] [-] darkr|10 years ago|reply
It's gradually morphed from being a Times for mildly xenophobic Conservatives (big C) into a Daily Mail for toffs.
[+] [-] cshimmin|10 years ago|reply
So... this is news before news? I.e. rumor. LIGO is not scheduled to announce results for another 3.5 hrs.
[+] [-] apsec112|10 years ago|reply
https://en.wikipedia.org/wiki/Martin_Rees
[+] [-] michaelhoffman|10 years ago|reply
[+] [-] agentgt|10 years ago|reply
[+] [-] unknown|10 years ago|reply
[deleted]
[+] [-] sgrytoyr|10 years ago|reply
[+] [-] Aeolos|10 years ago|reply
You can use "low-coherence interferometry" to measure tiny signals that would be undetectable otherwise. Combine a "reference" beam with a "signal" beam and you get a measurable interference pattern, even when the magnitude of the signal beam is miniscule.
This is what a real-life interference pattern looks like (I just acquired this from an actual interferometer illuminating a painted metal surface):
https://dl.dropboxusercontent.com/u/30682604/fringe_signal.p...
This is now an established medical imaging method (Optical Coherence Tomography) to create 3d scans of biological tissue. It can also be used to measure distance or elevation changes on a surface of anything from a micrometer-level scale to a planetary surface. All you need is to use light with the right wavelengths and two measurements "arms" of roughly the same length.
[+] [-] Velox|10 years ago|reply
[+] [-] bbrazil|10 years ago|reply
Basically fire two lasers at right angles to each other at mirrors, and see the pattern when they bounce back.
[+] [-] mclightning|10 years ago|reply
For example their electromagnetic fields may be shifting depending on distance to another atom or another field.
PS: I am no physicist.
[+] [-] merraksh|10 years ago|reply
[+] [-] ascorbic|10 years ago|reply
[+] [-] pavanky|10 years ago|reply
[+] [-] joolze|10 years ago|reply
Seriously, the only thing this article is says: Physicists and astronomers are agog. On Thursday, experimenters will report the first detection of a phenomenon that has been long predicted: bursts of gravitational waves generated by cosmic collisions of black holes.
That is NOT a report, that's someone guessing what the report will be. There's not a single quote from anyone remotely involved in the project. This is a piece of shit summary of a wikipedia entry on LIGO with a clickbait headline.
SAGE
[+] [-] apsec112|10 years ago|reply
"Sadly it is not unknown for hyped-up scientific claims to be mistaken or exaggerated - claims of particles going faster than light, gravitational waves from the big bang, and so forth. I count myself a hard-to-convince sceptic. But what is being claimed will be the culmination of literally decades of effort by scientists and engineers with high credentials, and this time I expect to be fully convinced."
ie., Sir Martin Rees (the author), one of the most famous astronomers in the world, is putting his credibility behind this. That matters.
[+] [-] graycat|10 years ago|reply
Still, back to common, ordinary, reality, Sir Rees does have a lot of credibility.
[+] [-] feider|10 years ago|reply
Sounds like a good old survival bias ;) Seriously though, what is confidence interval in LIGO?
[+] [-] roddux|10 years ago|reply
[+] [-] bakhy|10 years ago|reply
[+] [-] amelius|10 years ago|reply
[+] [-] MereInterest|10 years ago|reply
LIGO can only measure gravitational waves down to a certain strength, and so we can only detect waves that are caused by black hole mergers within some distance of Earth. Predictions of how many such mergers occur vary wildly, depending on the assumptions in the model. (I don't have exact numbers, and would appreciate if anyone does have the numbers.)
If we did not detect gravitational waves, I would use that as a lower bound of the number of black hole mergers, rather than as a breaking of general relativity.
[+] [-] olympus|10 years ago|reply
But this is still pretty spectacular in it's own right. The predictions that physicists make are made by examining mathematical models that are only partially vetted. Some parts of the models remain theoretical because we don't have instruments sensitive enough to measure their predictions (we are talking about energies on a ridiculous tiny scale here). Finally we have invested millions on an instrument that is sensitive enough and it confirms (to the best of its ability) that we were on the right track. This is a great relief to the scientists that they don't have to go back to the drawing board and rethink all their models, plus it is a great victory for predictions made before the age of computers.
[+] [-] dantillberg|10 years ago|reply
[0]: The Hulse–Taylor binary pulsar: https://en.wikipedia.org/wiki/PSR_B1913%2B16
[+] [-] agentgt|10 years ago|reply
The article says many expected LIGO to take much longer but it found it rather earlier equating it to beginners luck (I know the article is written for the layperson but it leaves much to be desired with that phrase).
You never know we could have telescopes that use Gravitational waves instead of light.
[+] [-] lobster_johnson|10 years ago|reply
[+] [-] ck2|10 years ago|reply
Are gravitational waves also limited to the same speed as light?
Wait, is it the actual fabric of space that is "waving" ? Whoa.
ps. fun fact "razzmatazz" appears in google less than a million times
[+] [-] MereInterest|10 years ago|reply
Since there are two such facilities, located on different parts of the Earth, they may be able to compare the relative size measured by each facility, and narrow down a part of the sky. Since the facilities are relatively close to each other (only 2000 miles, 30 degrees along Earth's circumference), the margin of error would be very large.
Ideally, to localize the direction, you would have three facilities, each located at 90 degrees away from the other two, so that you have one facility "pointed" in each direction. Even then, it would only be able to narrow it down to 2 possible origins, as the direction of travel of the wave would not be measurable.
Anything that carries information is limited to the speed of light. Gravitational waves carry information about the location of the merging black holes, and so they are limited to the speed of light. If anything that carried information were to travel faster than the speed of light, it would break causality, because you could find some frame of reference in which the effect happened before the cause.
And yes, it is spacetime itself that is vibrating.
[+] [-] kryptiskt|10 years ago|reply
[+] [-] dantillberg|10 years ago|reply
*: And this would also possibly serve to answer another question -- do gravitational waves travel at precisely the speed of light? (also, I'd be interested in hearing about neutrino detectors -- how closely (if nonzero) to the speed of light do neutrinos travel?)
[+] [-] joolze|10 years ago|reply
and yes, they can only exist if they travel at the speed of light. it's a major test of the limiting speed of light.
[+] [-] brnie4d1kt4tr|10 years ago|reply
Yes, the existance of grav waves is only possible if they travel at some top speed, which is presumed to be the speed of light.
[+] [-] kkamperschroer|10 years ago|reply
[+] [-] anotheryou|10 years ago|reply
press conference is streamed in an hour here: https://youtu.be/zyo4DFr4D4I
[+] [-] srikar|10 years ago|reply
[+] [-] antome|10 years ago|reply
[+] [-] hcrisp|10 years ago|reply
[+] [-] brnie4d1kt4tr|10 years ago|reply
[deleted]
[+] [-] amelius|10 years ago|reply
Or are these detectors already directionally sensitive?
[+] [-] Steuard|10 years ago|reply
[+] [-] ww520|10 years ago|reply
[+] [-] unknown|10 years ago|reply
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